Magnetic storage media, typically in the form of disks, are widely used in the computer industry to increase the amount of storage capacity beyond what is available in the computer's internal memory. While such devices greatly expand the storage capacity of the computer, the data stored in them cannot be retrieved as quickly or easily as data stored in,, for example, a random access memory (RAM).
Data are conventionally recorded on a disk in concentric tracks. A head reads the tracks and produces a serial, one-bit wide data stream. The data may then be passed through a shift register and converted into a parallel data stream. However, to retrieve data over an 8-bit (1 byte) parallel bus at 6 megabytes per second, the serial data must be read at 48' megabits per second. While this rate is achievable with today's technology, higher rates, for example, 60 or 100 megabits per second, stretch the capabilities of a serial data path. Thus the serial data path extending from the head represents a "bottleneck" which potentially limits the ability of the computer to retrieve data from the storage disk. Similar considerations apply to the write operation.
The term "track density" refers to the number of tracks which occupy a given radial distance on the disk; the track "pitch" is the reciprocal of the track density. In a typical low-cost Winchester disk, the track density is around 1000 tracks per inch, and densities of twice this value are achieved in more sophisticated drives. Obviously the quantity of information that can be stored is directly related to the track density.
Data are generally written to and read from the magnetic medium by means of a "gap", which refers to the separation between the tips of a pair of magnetic poles. One of the factors that has limited increases in the track density is the existence of cross-talk between adjacent tracks. During the reading operation, the gap tends to pick up data from adjacent tracks. This decreases the signal-to-noise ratio of the read channel, and increases the probability of errors in the interpretation of the data. Increasing the track density (i.e., reducing the track pitch) exacerbates this problem.
In the writing process, magnetic flux lines from the pole tip on one side of the gap extend downward, through the magnetic medium, and into the other pole tip. Ideally, the width of the pole tips should coincide with the width of the written data track. However, in reality some of the magnetic flux lines near the side edges and corners of the pole tips extend laterally outward beyond the edge of the track and create a "noise fringe" along the edge of the track. This noise fringe also limits the track density.
Various embodiments according to this invention provide for an increased rate of data transfer to and from a magnetic storage medium, and a reduction of the cross-talk and noise fringe problems.